An adhesive is a substance capable of holding solid materials (e.g., adherents or substrates) together by surface attachment. Adhesives have been widely used since ancient times. Archaeologists have found evidence of substances being used as adhesives in Babylon dating back to 4000 B.C. and in Egypt between 1500-1000 B.C. The first adhesive patent was issued in about 1750 in Britain for a glue made from fish. Later, patents were issued for adhesives using natural rubber, animal bones, fish, starch, milk protein or casein. The development of synthetic adhesives from the late 19th century has led to many synthetic adhesives, such as nitrocellulose, phenol-formaldehyde resins, urea-formaldehyde resins, epoxy resins, bismaleimide resins, polysiloxanes, polychloroprene, polyacrylates, polymethacrylates, polyurethanes, polycyanoacrylates, hot melt adhesives and pressure sensitive adhesives.
Pressure sensitive adhesives (PSAs) generally are adhesive materials which bond to adherents when a required pressure is applied to effect an adhesion to the adherents. PSAs can be permanent or removable. Removable PSAs have been widely used in re-positionable applications, such as post-it notes. Pressure sensitive adhesives are generally based on a polymer, a tackifier and an oil. Some common PSAs are based on polymers such as natural rubbers, synthetic rubbers (e.g., styrene-butadiene rubber (SBR) and SIS), polyacrylates, polymethacrylates, and poly-alpha-olefins. The PSAs can be solvent-based, water-based, or hot melt systems.
Hot-melt adhesives at ambient temperature are generally solid materials that can be heated to a melt to hold adherents or substrates together upon cooling and solidifying. In some applications, the bonded substrates can be detached by remelting the hot melt adhesive if the substrates can withstand the heat. The hot melt adhesives can be used in paper products, packaging materials, laminated wood panels, kitchen countertops, vehicles, tapes, labels, and a variety of disposable goods such as disposable diapers, hospital pads, feminine sanitary napkins, and surgical drapes. These hot melt adhesives are generally based on a polymer, tackifier, and a wax. Some common hot melt adhesives are based on polymer components including ethylene based semi-crystalline polymers such as ethylene-vinyl acetate copolymer (EVA) and linear low density polyethylene (LLDPE), styrene block copolymers (SBC) such as styrene-isoprene-styrene (SIS) copolymer and styrene-butadiene-styrene (SBS) copolymer, ethylene ethyl acrylate copolymers (EEA), and polyurethane reactive adhesives (PUR). One desirable property of hot melt adhesives is the absence of a liquid carrier, thereby eliminating the costly process associated with solvent removal.
Some compositions that contain a polymer, a tackifier and optionally at least a filler or a pigment may be used as thermoplastic marking compositions. The polymer can be a silane-modified petroleum resin, an ethylene-vinyl acetate copolymer, an atactic polypropylene; a carboxy-modified hydrocarbon resin, an ester-modified hydrocarbon resin, a polyolefin copolymer, or a combination thereof.
Despite the availability of a variety of hot melt adhesives, pressure sensitive adhesives, and road paints, there are still needs for new adhesive compositions with improved properties.